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Regardless of this fact, even the most conservative iPhone 4 user is going to have a day that pushes the limits of his or her phone's built-in 1420 mAh battery. The Juice Pack Plus from Mophie -- the same company that launched an iPhone-based credit card processing system earlier this year -- adds an additional 2000 mAh battery within its shell, bringing the total onboard power to 3420 mAh and extending iPhone 4 use times by a large margin.